As a mobile communication network in the related art, there are 2G (2nd Generation) network such as a GERAN and 3G (3rd Generation) network such as an UTRAN. In the conventional 2G/3G networks, both voice call and data communication services are provided, but 3.9G (3.9 Generation) network such as an E-UTRAN have been under review to realize a faster high-speed data communication. Since a main object of the 3.9G network is to provide a high-speed data communication service, to perform a voice call by paging the voice call service to a mobile communication terminal resident in the 3.9G network, as shown in FIG. 9, it is necessary that when a voice call paging is received from a network (S901 of FIG. 9), mobile communication network in which the mobile communication terminal is resident needs to be transitioned from the 3.9G network to the 2G/3G network (S902 of FIG. 9), makes a response on the voice call to the network via 2G/3G network (S903 of FIG. 9) and receives the voice call service using the 2G/3G network (S904 of FIG. 9). Such switching of the mobile communication network is referred to as CS (Circuit Switched) fallback (see Non patent Literature 1), and a CS fallback-compatible mobile communication terminal has been developed.